GASTRIC DIGESTION. 419 



whilst in Man, hydrochloric acid is the chief source of the acidity, lactic acid 

 may be so in the dog and pig. Acetic, butyric, and phosphoric acids have also 

 been occasionally met with in the gastric fluid ; but they can scarcely be reckoned 

 among its normal constituents. 



442. The peculiar organic "ferment" of the gastric juice, to which the name 

 of Pepsin has been given, was first obtained in an isolated state by Wasmann; 

 who has given the following account of the properties and reactions of that 

 which he procured from the mucous membrane of the stomach of the Pig, which 

 greatly resembles that of Man. When this membrane is digested in a large 

 quantity of water at from 85 to 95, many other matters are removed from it 

 besides pepsin; but if this water be poured off, and the digestion be continued 

 with fresh water in the cold, very little but pepsin is then taken up. Pepsin 

 appears to be but sparingly soluble in water; when its solution is evaporated to 

 dryness, there remains a brown, grayish, viscid mass, with the odor of glue, and 

 having the appearance of an extract. The solution of this in water is turbid, 

 and still possesses a portion of the characteristic power of pepsin, but greatly 

 reduced. When strong alcohol is added to a fresh solution of pepsin, the latter 

 is precipitated in white flocks, which may be collected on a filter, and produce a 

 gray compact mass when dried. Pepsin enters into chemical combination with 

 many acids, forming compounds which still redden litmus paper ; and it is when 

 thus united with acetic and muriatic acids, that its solvent powers are the great- 

 est. 1 The general result of later inquiries has been to confirm the views laid 

 down in the following statement of Wasmann' s inquiries: "In regard to the 

 solvent power of pepsin for coagulated albumen, it was observed by M. Wasmann 

 that a liquid which contains 17-10,000ths of acetate of pepsin, and 6 drops of 

 hydrochloric acid per ounce, possesses a very sensible solvent power, so that it 

 will dissolve a thin slice of coagulated albumen in the course of six or eight hours' 

 digestion. With 12 drops of hydrochloric acid per ounce, the white of egg is 

 dissolved in two hours. A liquid which contains gr. of acetate of pepsin, and 

 to which hydrochloric acid and white of egg are alternately added, so long as 

 the latter dissolves, is capable of taking up 210 grains of coagulated white of 

 egg at a temperature between 95 and 104. It would appear, from such ex- 

 periments, that the hydrochloric acid is the true solvent, and that the action of 

 the pepsin is limited to that of disposing the white of egg to dissolve in hydro- 

 chloric acid. The acid when alone dissolves white of egg by ebullition, just as 

 it does under the influence of pepsin ; from which it follows that pepsin replaces 

 the effect of a high temperature, which is not possible in the stomach. The 

 same acid with pepsin dissolved blood, fibrin, meat and cheese ; while the isolated 

 acid dissolved only an insignificant quantity at the same temperature; but when 

 raised to the boiling point, it dissolved nearly as much, and the part dissolved 

 appeared to be of the same nature. The epidermis, horn, the elastic tissue 

 (such as the fibrous membrane of arteries) do not dissolve in a dilute acid con- 

 taining pepsin. M. Wasmann has remarked that the pepsin of the stomach of 

 the pig is entirely destitute of the power to coagulate milk, although the pepsin 

 of the stomach of the calf possesses it in a very high degree; from which he is 

 led to suppose, that the power of the latter depends upon a particular modifica- 



1 It has been supposed by Prof. Schmidt (of Dorpat), that the union of pepsin with these 

 and other acids forms a "conjugated" acid ( 58, note], which possesses the property of 

 forming soluble compounds with albuminous and other azotized substances ; but the ex- 

 istence of such an acid has not been determined by the analysis of any combination either 

 with a mineral base or with an albuminous substance ; and the numerous experiments 

 which have been made by Prof. Lehmann regarding the digestive agents and substances 

 to be digested, indicate no such definite proportion between them, as this view of the con- 

 stitution of the former would require. 



